PhotoShop图层混合模式的Canvas实现

前端开发人员可能会遇到这样一个问题。

当设计人员给到一个PSD以后，会发现其中有些图层是有图层混合效果的。

这样会产生一个情况就是，我们为了这个效果而不得不将背景+带混合的图层切到一起。

当这样的元素多了以后，我们所切出的图片就会越来越大并且难以修改。

那么，本章我们将讲解如何使用Canvas元素来实现混合模式。

以达到减少图片体量和数量的效果。

首先，我们来讲一下基本实现原理。

大家可能都知道，Canvas是位图处理，Svg是矢量处理。那么什么是位图，什么是矢量图呢？

请看以下图片进行对比：



图像引用自互联网，原文地址：http://jingyan.baidu.com/album/54b6b9c0dbef682d583b4722.html?picindex=2

从上图可知，100%大小的矢量图在缩放到800%的时候并没有出现失真的情况，即：没有马赛克。

而位图则出现了万恶的马赛克，图像已经变得模糊不清了。

那么，为什么我们要使用Canvas呢？

因为网上太多类似的文章了，所以这里直接外链。

就本章节的内容来说，我们使用Canvas是为了使用像素处理。

为了方便读者实践，这里给出两张实验图片。（图片取自网络，请勿用于商业用途，如有侵犯请联系本人进行处理，感激不尽）


原图（假设图片名为：background.jpg）


混合图（假设图片名为：butterfly.png）

实现效果的前置代码：

// 指定要使用的处理器，这里暂时不指定
var processor = "";
// 所有的处理器都在这个对象下
var pixProcessor = {};

var imgBackground = new Image();
var imgButterfly = new Image();
imgBackground.onload = imgButterfly.onload = function () {
this.loaded = true;
if (imgBackground.loaded && imgButterfly.loaded) {
process();
}
};
imgBackground.src = "background.jpg";
imgButterfly.src = "butterfly.png";

var canvas = document.createElement("canvas");
canvas.width = 610;
canvas.height = 502;
var context = canvas.getContext("2d");

以上代码十分好理解。

1.将两张图片加载进来。

2.创建一个canvas元素并获取其context。

3.图片加载完成后触发名为process的函数。

好的，现在我们来仔细看看process函数里都做了什么操作。

function process() {
// 计算蝴蝶图片相对背景图片的中心位置
var centerX = (imgBackground.width - imgButterfly.width) / 2;
var centerY = (imgBackground.height - imgButterfly.height) / 2;

// 绘制背景图
context.drawImage(imgBackground, 0, 0);
// 通过getImageData函数获取背景图片中，蝴蝶图片所应该在的区域的像素数据
var backgroundData = context.getImageData(centerX, centerY, imgButterfly.width, imgButterfly.height);
// 缓存ImageData中的data数组，这才是我们要操作的东西
var backgroundPixs = backgroundData.data;

// 清空一次画布
context.clearRect(0, 0, canvas.width, canvas.height);

// 绘制蝴蝶图
context.drawImage(imgButterfly, centerX, centerY);
// 不解释
var butterflyData = context.getImageData(centerX, centerY, imgButterfly.width, imgButterfly.height);
// 不解释
var butterflyPixs = butterflyData.data;

// 再次绘制背景图
context.drawImage(imgBackground, 0, 0);
// 再次绘制蝴蝶图（反正这句话也没什么卵用，忘了当时为啥要写这句话了）
context.drawImage(imgButterfly, centerX, centerY);

// 若没有定义处理器则不进行处理
if (typeof processor != "undefined") {
var newPix;
for (var i = 0; i < backgroundPixs.length; i += 4) {
// 跳过全透明像素
if (butterflyPixs[i + 3] == 0) continue;

// 传入两个图像对应的像素进行处理
newPix = pixProcesser[processor]({ red: backgroundPixs[i], green: backgroundPixs[i + 1], blue: backgroundPixs[i + 2], alpha: backgroundPixs[i + 3] },
{ red: butterflyPixs[i], green: butterflyPixs[i + 1], blue: butterflyPixs[i + 2], alpha: butterflyPixs[i + 3] });

if (newPix) {
// 将处理好的像素赋值给背景图ImageData（实际上你传给蝴蝶图也没问题，只是下面putImageData的时候需要指向蝴蝶图罢了）
backgroundPixs[i] = newPix.red;
backgroundPixs[i + 1] = newPix.green;
backgroundPixs[i + 2] = newPix.blue;
}
}

// 好的，将处理结果交给浏览器
context.putImageData(backgroundData, centerX, centerY);
}
if (document.body) {
document.appendChild(canvas);
} else {
window.addEventListener("load", function () {
document.appendChild(canvas);
}, false);
}
}

好的，现在我们进入华丽时间！~

1.正常模式，processor需要指定为
normal

pixProcesser.normal = function (background, butterfly) {
/// <summary>正常模式</summary>

var alpha = butterfly.alpha;
return {
red: butterfly.red * alpha + background.red * (1 - alpha),
green: butterfly.green * alpha + background.green * (1 - alpha),
blue: butterfly.blue * alpha + background.blue * (1 - alpha),
alpha: butterfly.alpha * alpha + background.alpha * (1 - alpha)
}
};

2.溶解，processor需要指定为 dissolve

pixProcesser.dissolve: function (background, butterfly) {
/// <summary>溶解</summary>

// 正式用判断条件
//if (Math.floor(Math.random() * 100) > (butterfly.alpha / 255 * 100)) {

// 测试用判断条件
if (Math.floor(Math.random() * 100) > 50) {
return background;
} else {
return butterfly;
}
};

3.变暗，processor需要指定为 darken

pixProcesser.darken: function (background, butterfly) {
/// <summary>变暗</summary>

return {
red: Math.min(background.red, butterfly.red),
green: Math.min(background.green, butterfly.green),
blue: Math.min(background.blue, butterfly.blue),
alpha: Math.min(background.alpha, butterfly.alpha)
};
};

4.正片叠底，processor需要指定为 multiply

pixProcesser.multiply: function (background, butterfly) {
/// <summary>正片叠底</summary>

return {
red: butterfly.red * background.red / 255,
green: butterfly.green * background.green / 255,
blue: butterfly.blue * background.blue / 255,
alpha: butterfly.alpha * background.alpha / 255
};
};

5.颜色加深，processor需要指定为 colorBurn

pixProcesser.colorBurn: function (background, butterfly) {
/// <summary>颜色加深</summary>

return {
red: Math.max(0, background.red + butterfly.red - 255) * 255 / butterfly.red,
green: Math.max(0, background.green + butterfly.green - 255) * 255 / butterfly.green,
blue: Math.max(0, background.blue + butterfly.blue - 255) * 255 / butterfly.blue,
alpha: Math.max(0, background.alpha + butterfly.alpha - 255) * 255 / butterfly.alpha
};
};

6.线性加深，processor需要指定为 linearBurn

pixProcesser.linearBurn: function (background, butterfly) {
/// <summary>线性加深</summary>

return {
red: Math.max(0, background.red + butterfly.red - 255),
green: Math.max(0, background.green + butterfly.green - 255),
blue: Math.max(0, background.blue + butterfly.blue - 255),
alpha: Math.max(0, background.alpha + butterfly.alpha - 255)
};
};

7.深色，processor需要指定为 darkerColor

pixProcesser.darkerColor: function (background, butterfly) {
/// <summary>深色</summary>

if ((background.red + background.green + background.blue + background.alpha) < (butterfly.red + butterfly.green + butterfly.blue + butterfly.alpha)) {
return background;
} else {
return butterfly;
}
};

8.变亮，processor需要指定为 lighten

pixProcesser.lighten: function (background, butterfly) {
/// <summary>变亮</summary>

return {
red: Math.max(background.red, butterfly.red),
green: Math.max(background.green, butterfly.green),
blue: Math.max(background.blue, butterfly.blue),
alpha: Math.max(background.alpha, butterfly.alpha)
};
};

9.滤色，processor需要指定为 screen

pixProcesser.screen: function (background, butterfly) {
/// <summary>滤色</summary>

return {
red: 255 - (255 - butterfly.red) * (255 - background.red) / 255,
green: 255 - (255 - butterfly.green) * (255 - background.green) / 255,
blue: 255 - (255 - butterfly.blue) * (255 - background.blue) / 255,
alpha: 255 - (255 - butterfly.alpha) * (255 - background.alpha) / 255
};
};

10.颜色减淡，processor需要指定为 colorDodge

pixProcesser.colorDodge: function (background, butterfly) {
/// <summary>颜色减淡</summary>

return {
red: background.red + butterfly.red * background.red / (255 - butterfly.red),
green: background.green + butterfly.green * background.green / (255 - butterfly.green),
blue: background.blue + butterfly.blue * background.blue / (255 - butterfly.blue),
alpha: background.alpha + butterfly.alpha * background.alpha / (255 - butterfly.alpha)
};
};

11.线性减淡，processor需要指定为
linearDodge

pixProcesser.linearDodge: function (background, butterfly) {
/// <summary>线性减淡</summary>

return {
red: Math.min(background.red + butterfly.red, 255),
green: Math.min(background.green + butterfly.green, 255),
blue: Math.min(background.blue + butterfly.blue, 255),
alpha: Math.min(background.alpha + butterfly.alpha, 255)
};
};

12.浅色，processor需要指定为 lighterColor

pixProcesser.lighterColor: function (background, butterfly) {
/// <summary>浅色</summary>

if ((background.red + background.green + background.blue + background.alpha) > (butterfly.red + butterfly.green + butterfly.blue + butterfly.alpha)) {
return background;
} else {
return butterfly;
}
};

13.叠加，processor需要指定为 overlay

pixProcesser.overlay: function (background, butterfly) {
/// <summary>叠加</summary>

return {
red: 255 - (255 - butterfly.red) * (255 - background.red) / 128,
green: 255 - (255 - butterfly.green) * (255 - background.green) / 128,
blue: 255 - (255 - butterfly.blue) * (255 - background.blue) / 128,
alpha: 255 - (255 - butterfly.alpha) * (255 - background.alpha) / 128
};
};

14.柔光，processor需要指定为 softLight

pixProcesser.softLight: function (background, butterfly) {
/// <summary>柔光</summary>

return {
red: background.red + (2 * butterfly.red - 255) * (Math.sqrt(background.red / 255) * 255 - background.red) / 255,
green: background.green + (2 * butterfly.green - 255) * (Math.sqrt(background.green / 255) * 255 - background.green) / 255,
blue: background.blue + (2 * butterfly.blue - 255) * (Math.sqrt(background.blue / 255) * 255 - background.blue) / 255,
alpha: background.alpha + (2 * butterfly.alpha - 255) * (Math.sqrt(background.alpha / 255) * 255 - background.alpha) / 255
};
};

15.强光，processor需要指定为 hardLight

pixProcesser.hardLight: function (background, butterfly) {
/// <summary>强光</summary>

return {
red: butterfly.red > 128 ? 255 - (255 - butterfly.red) * (255 - background.red) / 128 : butterfly.red * background.red / 128,
green: butterfly.green > 128 ? 255 - (255 - butterfly.green) * (255 - background.green) / 128 : butterfly.green * background.green / 128,
blue: butterfly.blue > 128 ? 255 - (255 - butterfly.blue) * (255 - background.blue) / 128 : butterfly.blue * background.blue / 128,
alpha: butterfly.alpha > 128 ? 255 - (255 - butterfly.alpha) * (255 - background.alpha) / 128 : butterfly.alpha * background.alpha / 128
};
};

16.亮光，processor需要指定为 vividLight

pixProcesser.vividLight: function (background, butterfly) {
/// <summary>亮光</summary>

return {
red: butterfly.red <= 128 ? 255 - (255 - background.red) / (2 * butterfly.red) * 255 : background.red / (2 * (255 - butterfly.red)) * 255,
green: butterfly.green <= 128 ? 255 - (255 - background.green) / (2 * butterfly.green) * 255 : background.green / (2 * (255 - butterfly.green)) * 255,
blue: butterfly.blue <= 128 ? 255 - (255 - background.blue) / (2 * butterfly.blue) * 255 : background.blue / (2 * (255 - butterfly.blue)) * 255,
alpha: butterfly.alpha <= 128 ? 255 - (255 - background.alpha) / (2 * butterfly.alpha) * 255 : background.alpha / (2 * (255 - butterfly.alpha)) * 255
};
};

17.线性光，processor需要指定为 linearLight

pixProcesser.linearLight: function (background, butterfly) {
/// <summary>线性光</summary>

return {
red: Math.min(2 * butterfly.red + background.red - 255, 255),
green: Math.min(2 * butterfly.green + background.green - 255, 255),
blue: Math.min(2 * butterfly.blue + background.blue - 255, 255),
alpha: Math.min(2 * butterfly.alpha + background.alpha - 255, 255)
};
};

18.点光，processor需要指定为 pinLight

pixProcesser.pinLight: function (background, butterfly) {
/// <summary>点光</summary>

if (typeof pixProcesser.pinLightProcess == "undefined") {
pixProcesser.pinLightProcess = function (sourceColor, blendColor) {
return blendColor <= 128 ? Math.min(sourceColor, 2 * blendColor) : Math.max(sourceColor, 2 * blendColor - 255);
};
}

return {
red: pixProcesser.pinLightProcess(background.red, butterfly.red),
green: pixProcesser.pinLightProcess(background.green, butterfly.green),
blue: pixProcesser.pinLightProcess(background.blue, butterfly.blue),
alpha: pixProcesser.pinLightProcess(background.alpha, butterfly.alpha)
};
};

19.实色混合，processor需要指定为 hardMix

pixProcesser.hardMix: function (background, butterfly) {
/// <summary>实色混合</summary>

return {
red: (background.red + butterfly.red) < 255 ? 0 : 255,
green: (background.green + butterfly.green) < 255 ? 0 : 255,
blue: (background.blue + butterfly.blue) < 255 ? 0 : 255,
alpha: (background.alpha + butterfly.alpha) < 255 ? 0 : 255
};
};

20.差值，processor需要指定为 difference

pixProcesser.difference: function (background, butterfly) {
/// <summary>差值</summary>

return {
red: Math.abs(butterfly.red - background.red),
green: Math.abs(butterfly.green - background.green),
blue: Math.abs(butterfly.blue - background.blue),
alpha: Math.abs(butterfly.alpha - background.alpha),
};
};

21.排除，processor需要指定为 exclusion

pixProcesser.exclusion: function (background, butterfly) {
/// <summary>排除</summary>

return {
red: (butterfly.red + background.red) - butterfly.red * background.red / 128,
green: (butterfly.green + background.green) - butterfly.green * background.green / 128,
blue: (butterfly.blue + background.blue) - butterfly.blue * background.blue / 128,
alpha: (butterfly.alpha + background.alpha) - butterfly.alpha * background.alpha / 128
};
};

22.减去，processor需要指定为 subtract

pixProcesser.subtract: function (background, butterfly) {
/// <summary>减去</summary>

return {
red: Math.max(0, background.red - butterfly.red),
green: Math.max(0, background.green - butterfly.green),
blue: Math.max(0, background.blue - butterfly.blue),
alpha: Math.max(0, background.alpha - butterfly.alpha)
};
};

23.划分，processor需要指定为 divide

pixProcesser.divide: function (background, butterfly) {
/// <summary>划分</summary>

return {
red: (background.red / butterfly.red) * 255,
green: (background.green / butterfly.green) * 255,
blue: (background.blue / butterfly.blue) * 255,
alpha: (background.alpha / butterfly.alpha) * 255,
};
};

至此完成。您可以自己动手实验啦~~~

非常感谢您的阅读！您的支持是我的动力！